In wireless devices, and especially battery-powered mobile devices such as mobile phones, smart phones, tablets and laptops, it is desirable to minimise the power consumption of the device so as to conserve battery life. There may also be other motivations such as limiting the heat generated, which may in turn allow slimmer packaging or cheaper components to be used.
One main subsystem incurring significant power consumption in a wireless device is the radio front-end of the wireless transceiver. On the transmit path this may comprise components such as a power amplifier (PA), a digital-to-analogue converter (DAC) and an up-conversion mixer. On the receive path this may comprise components such as a low-noise amplifier (LNA), an analogue to digital converter (ADC), and a down-conversion mixer. The power amplifier in particular can be the cause of a large portion of the power consumption of the device.
In order to conserve power, it is known to provide the radio transceiver with a mechanism allowing it to be powered down when not in use. The powering up and down of the radio is typically controlled by driver layer software, by writing to a software accessible register arranged to toggle the state of the radio transceiver. The powering down itself may comprise for example switching off a power supply connection to one of the components of the radio transceiver such as the power amplifier, e.g. because such components may draw current even when not being used to transmit or receive signals. The details of the power-down mechanism may vary, but the programmer of the driver software need not necessarily concern him or herself with such details—all he or she needs to know is that when a certain value is written to the relevant register then the radio transceiver is placed into a higher-power state in which it is readied for transmission and/or reception of radio traffic (at the expense of higher power consumption), and that when a certain other value is written to the register then the radio transceiver is placed into a lower-power state in which it is not able to transmit and/or receive radio traffic (in favour of reduced power consumption).
However, the powering up and down operation takes a finite amount of time, and also may itself incur a certain power consumption due to surges in current when turning the radio on or off. Hence it is not generally desirable to turn the radio on and off too frequently.
One regime for controlling the radio is to turn off the radio when triggered by a time-out, i.e. after a certain predetermined period of radio inactivity. However, this has the disadvantage that sporadic traffic could still keep the radio switched on for long amounts of time if each subsequent message keeps falling within the predetermined period.
Another possibility could be for the driver software to queue traffic so as to attempt to transmit and/or receive messages together in bursts, thus allowing more opportunities for powering down the radio between bursts. However, this could have the disadvantage that time-critical traffic could be delayed by an intolerable amount.